The specific aim of this proposal is to conduct the Fourth International Conference on Limb Development and Regeneration, emphasizing advances that have occurred over the past 10 years in our understanding of the cellular and molecular mechanisms of these processes. The meeting will be 4.5 days in length, with a keynote speaker leading off each day. Approximately 125 presentations are anticipated in oral and poster sessions, covering the topics of formation of the regeneration blastema, growth of the limb bud and blastema, and the patterning of these structures. Sessions on limb bud growth and blastema formation and growth will include the expression and function of (1) ECM molecules; (2) growth factors; and (3) oncogenes. Sessions on pattern formation will include (1) retinoids; (2) role of retinoid receptors and cellular retinoic acid binding protein; (3) expression and function of homeobox and other patterning genes, and (4) the developmental genetics of limb patterning. The role of tissue interactions in orchestrating molecular expression during growth and pattern formation will be emphasized throughout. Developmental anomalies and differences between limb development and regeneration will receive special consideration. The conference is expected to appeal to basic scientists in the areas of cell and developmental biology, graduate students and postdocs, clinicians and scientists in the biopharmaceutical industry.